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The synaptic connection between two neurons is represented as a “synapse type”
class. Note that synaptic attributes that belong solely to the post-synaptic
neuron, such as the decay of the post-synaptic conductance, are part of the
cell type model. The “synapse type” models the synaptic delay, the synaptic
weight, and any dynamic behaviour of the synaptic weight, i.e. synaptic
plasticity.

As for cell types, PyNN has a library of “standard” synapse types that should
give the same behaviour on different simulators, and also supports the use of
“native” synapse types, limited to a single simulator.

A specification for an STDP mechanism, combining a weight-dependence, a
timing-dependence, and, optionally, a voltage-dependence of the synaptic
change.

For point neurons, the synaptic delay d can be interpreted either as
occurring purely in the pre-synaptic axon + synaptic cleft, in which
case the synaptic plasticity mechanism ‘sees’ the post-synaptic spike
immediately and the pre-synaptic spike after a delay d
(dendritic_delay_fraction = 0) or as occurring purely in the post-
synaptic dendrite, in which case the pre-synaptic spike is seen
immediately, and the post-synaptic spike after a delay d
(dendritic_delay_fraction = 1), or as having both pre- and post-
synaptic components (dendritic_delay_fraction between 0 and 1).

In a future version of the API, we will allow the different
components of the synaptic delay to be specified separately in
milliseconds.